Handrail guide system for passenger conveyor

ABSTRACT

A stationary substantially continuous guide forming a closed guide loop eliminates the need for tensioning a passenger conveyor handrail and permits it to be pushed as well as pulled around the guide loop. A flexible portion of the guide may be bowed to adjust the length of the guide loop to the exact length of the handrail.

United States Patent 1191 Boltrek et al. 1 Jan. 23, 1973 1 HANDRAIL UIDE Y TEM FOR 3,568,813 3/1971 Schaeffer ..l98/l6 PASSENGER CONVEYOR 1,227,005 5/1917 Search ..l98/208 3,170,557 2 1965 T k t 1.... ""1198 16 [761 Inventors: Henry 15 wflshire 2929 483 3l960 .19816 Freeport, NY. 11520; Menno E. l Hill, 17 Highfield Lane, Rutherford, FOREIGN PATENTS OR APPLICATIONS NJ. 07070; Joseph K. Kraft, 223 'p Avenue, Verona NJ 247,236 5/1966 Austria ..l98/16 07044' Ernest J. Schirmer 67 Primary ExaminerEvon C. Blunk E tt S N.

Vere fleet Closter' J 07624 Assistant ExaminerMer1e F. Maffei 1 Filedl Feb-17,1971 Attorney-A. T. Stratton, C. L. Freedman and R. V. 21 Appl. No.: 116,264 weseflwff Related U.S. Application Data [57] ABSTRACT [63] Continuation f Ser, N 805,135, M h 7, 1969, A stationary substantially continuous guide forming a abandoned. closed guide loop eliminates the need for tensioning a passenger conveyor handrail and permits it to be [52] U.S. C1 pushed as well as pulled around the guide loop A flex- [51] Int. Cl. ..B66b 9/12 ible portion of the guide may be bowed to adjust the [58] Field of Search ..198/l6, 208 l h f the guide loop to the exact length of the handrail. [56] References Cited UNITED STATES PATENTS 8/1962 Fabula ..l98/l6 9 Claims, 6 Drawing Figures HANDRAIL GUIDE SYSTEM FOR PASSENGER CONVEYOR CROSS REFERENCE TO RELATED APPLICATION This application is a continuation of application Ser. No. 805,135, filed Mar. 7, 1969, now abandoned, which was assigned to the same assignee as the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to passenger conveyors of the moving-belt type, and has particular relation to such conveyors having moving handrails operating in synchronism with the conveyor belt.

2. Description of the Prior Art Moving-belt passenger conveyors may take the form of moving stairways or moving sidewalks. It is common practice and a Safety Code Requirement in such apparatus to provide at each side of the belt a continuous or endless flexible handrail in the form of an elongated loop having an upper run to be grasped by conveyor passengers. The loop also has a lower or return run and its upper and lower runs are interconnected by curved end portions.

Conventionally the handrail is constructed with a C- shaped cross-section and is supported on its upper run by a generally T-shaped stationary guide fastened to the upper surface of the balustrade. Other constructions are utilized or have been proposed but this is the most widely used form. Large newel wheels serve as guides for the curved end portions as shown in U.S. Pat.

No. 2,885,057. Usually at least one of these newel wheels is connected to the conveyor whereby the handrail is driven in synchronism with the conveyor. The lower or return run of the handrail is usually supported at various points by guide wheels in accordance with a number of schemes.

According to the prior art, it has consistently been the practice to apply tension to the handrail primarily to obtain the tractive force necessary to pull the handrail around the guide loop and to eliminate the need for a continuous guide on the lower return run. Normally the tension has been applied by apparatus tending to increase the length of the lower return run. Since the handrail is usually made of an elastomer such as rubber, the handrail tends to stretch under tension despite-the reinforcing materials such as cotton fabric or canvas imbedded in the rubber. Often steel reinforcement such as high tensile wires or steel strip is molded into the handrail to prevent stretch. The tensioning of the handrail causes excessive wear on the handrail as it moves over the stationary guide and makes it imperative-that a moving guide be provided in the end portions where the handrail must negotiate curves of relatively small radii. This problem was fully appreciated when it became fashionable to provide transparent balustrades and the newel wheels were eliminated. It was found that even with numerous small wheels distributed around the curved end portions as in U.S. Pat. No. 3,049,213, excessively high driving forces were required and the excessive wear on the handrail was unacceptable. In addition the utilization of numerous small guide wheels raises the cost of the handrail system considerably and requires frequent maintenance to clean the wheels of debris to insure free turning.

SUMMARY or THE INVENTION According to the invention a continuous guide supports a passenger conveyor handrail over essentially its entire length thereby eliminating the necessity to maintain tension on the handrail. As a result, the handrail can be pushed as well as pulled around the closed guide loop thereby reducing the tensile loading on any particular section of the handrail. Furthermore, since the handrail is pulled halfway around the guide loop and is pushed the other half, it is alternately under moderate tension followed by moderate compression which puts less strain on the handrail than conventional systems wherein the handrail is subjected to higher tensile forces continuously. This increases the life of the handrail and greatly reduces the tendency to stretch during prolonged use thereby eliminating the need to mold high tensile wires into the handrail. A reduction in the loading on the handrail also reduces the frictional forces on the handrail as it negotiates the small radius curvatures at the ends of the conveyor and therefore eliminates the necessity to provide rollers to assist the handrail around these curves. The elimination of all moving parts from the handrail guide system, except of course for the driving. means, simplifies the construction and upkeep of the system which in turn reduces the cost.

The reduction in the tensile loading on a handrail of a given length of course increases the length of handrail that can be driven with a given tensile force. Furthermore, since the handrail does not have to be put under static tension, driving forces canbe applied at more than one point on the handrail without having the tensioning force reduce the tractive force at one driving point as it does under the conventional handrail driving scheme.

Preferably the guide is made in the form of an extruded member having oppositely disposed flanges which restrain the conventional C-shaped handrail. The extrudedguide member can be bent to form the curvature at the ends of-theconveyor. Since the loading on the handrail is greatly reduced over that in a handrail which is under tension, satisfactory operation is achieved with the handrail contacting the smooth surfaces of the flanges on the guide member directly. However, longerIwear can be realized by fitting U- shaped strips of a low friction material such as nylon over the flanges on the guide member. By extending one leg of the U-shaped strips and providing alip on it, the strip of low friction material can be snapped into place.

In order to adjust thelength of the guide loop to that of a'particular handrail or to accommodate for stretch, a portion of the guide is constructed of a flexible-yet stiff material-which can be bowed to lengthen the guide loop. Although bowing of the flexible portion leaves a slight gap in the guide loop, the amount of adjustment normally necessary would not affect the essential operation of the system.

It is therefore a first object of the invention to provide an improved handrail guide system for a passenger conveyor.

It is a second object of the invention to provide an improved handrail guide system for a passenger conveyor which eliminates all moving parts.

It is a third object of the invention to provide an improved handrail guide system of the type described in the previous object which has means of adjustment for variations in the lengths of particular handrails.

It is a fourth object of the invention to provide an improved handrail guide system which reduces the wear and stretch of the handrail permitting longer handrail I'UIIS.

It is afifth object of the invention to provide an improved handrail guide system which pennits the handrail to be driven at multiple driving points efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view in front elevation of a transportation device embodying the invention;

FIG. 2 is a detailed view in cross-section taken along the lines II-II;

FIG. 3 is a plan view taken along the lines III-III of a detail of the device shown in FIG. 1;

FIG. 4 is a detailed view with some parts in cross-section taken along line IV-IV of FIG. 3;

FIG. 5 is a detailed view in cross section taken along line VV of FIG. 1; and

FIG. 6 is a detailed view in cross-section of a modification of the portion-of the device shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, FIG. 1 shows a transportation device employing a conveyor 1 for transporting passengers between a first landing 2 and a second landing 3. The conveyor 1 desirably may be of the endless type conventionally employed in 'moving stairways or in moving walks. If the conveyor is employed in a moving walk it may take the form of a belt-type treadway or a pallet-type treadway. For present purposes, it will be shown that the conveyor 1 is employed in a moving stairway. The conveyor 1 has an upper load bearing run 1a on which passengers stand while being transported between the landings, and a lower return run 1b.

The conveyor moves in a closed path which extends around sprocket wheels 4 and 5 in a conventional manner. The upper sprocket wheel 4 may be rotated by an electric motor 6 through a suitable driving mechanism including a chain 7.

Above the conveyor 1 is a balustrade 8 for supporting a handrail 9. Usually a handrail is provided for each side of the conveyor. By referring to FIG. 2 it can be seen that the handrail 9 is C-shaped in cross-section with a base portion 9a and legs 9b each with a lip 9c. The handrail 9 is in the form of a closed loop and is mounted with the opening of the C disposed towards the center of the loop whereby the base 9a of the handrail is available to be grasped by passengers on the stairway.

The handrail 9 is guided in its closed loop by the continuous guide member 11. The guide member has an upper portion which extends along the upper surface of the balustrade 11a, a lower section 11b, two end sections 11c and d and a flexible section 113. Portions of the handrail 9 have been removed in FIG. 1 to expose various portions of the guide member 11. The guide member 1 1 forms a continuous guide for the handrail 9 except for the section between lle and 11f where the handrail passes through the driving mechanism 51 and except for the small gap 11h which will be described in more detail below.

The guide member 11 may be of the conventional T- shape or Y-shape commonly in use today. Alternatively the guide member may be U-shaped as shown in crosssection in FIG. 2 with vertical legs 13 ending in horizontal flanges 15. Such a U-shaped guide member can be extruded from aluminum, stainless steel or practically any metal or non-metallic material which can be easily bent to follow the contours of the balustrade. Guide member 11 is secured to the balustrade 8 at various points along its length by bolt 17 secured by nut 19.

It can be seen from FIG. 2 that the lips 9c of the handrail 9 fit over the flanges 15 of the guide member 11 to restrain the handrail to the path formed by the guide member. As was mentioned above, the loading on the handrail is such that satisfactory wearing is experienced with the hand rail 9 running in direct contact with the flanges 15 of the guide member 11. However, even longer wear may be realized by placing strips of material having low friction characteristics over the flanges 15. A U-shaped nylon strip such as strip 21 shown in FIG. 2 has been found to be satisfactory for this purpose. By extending one leg of the U-shaped nylon strip 21 and forming a lip 22 on the end of this extended leg, the nylon strip may be snapped into place over the flange 15 as shown in FIG. 2.

In order to provide that the overall length of the guide loop formed by the guide member may be adjusted to the exact length of the handrail 9, a portion of the guide member is made flexible as indicated at 11g in FIG. 1. The adjustment is provided by constructing a portion of the guide member of a flexible yet stiff material. This portion of the guide member is rigidly connected to the supporting structure 23 below the balustrade 8 at a point 23a. The other end of this flexible portion of the guide member is connected to the supporting structure at a variable point 23b. A cross-section of the flexible portion of the guide member 11 is shown in FIG. 4. Projecting from the base 25 are two short legs 27 which are surmounted by horizontal flanges 29. The shallow depth of this portion of the guide member permits it to be bowed easily. It should be made of material which will flex easily but will maintain'its bowed shape against the moderate forces exerted by the handrail tending to collapse the bowed.

portion. Polyvinyl has been found to be suitable for this purpose and a light gauge metal guide such as extruded aluminum has been found to be even more satisfactory since it will dissipate the heat generated by friction more readily, especially on long runs.

The movable end of the flexible portion of the guide member 11g is connected to the supporting structure 23 by bolts 3l passing through the slot 37 in the supporting member and secured by nuts 33 as can be seen from FIGS. 3 and 4. A sleeve 35 spaces the guide member 113 from the supporting structure 23 so that the lips 9c of the handrail clear the supporting structure. It can be seen from FIG. 3 that the amount of bow in the flexible section 11g can be varied by varying the position of the bolts 31 with respect to the slot 37. In order to bow the flexible portion 113 of the guide member, the bolts 31 are moved to the right in FIG. 3 with respect to the slot 37. This will increase the total length of the guide loop. The extra length comes from a gap 11h between the ends of the flexible portion 11g and the fixed portion of the return run of the guide member. This gap in the guide loop is normally not large enough to interfere with the operation of the guide rail system since the handrail itself has a certain amount of stiffness. It should be appreciated that the amount of bow shown in FIG. 1 has been exaggerated for purposes of illustration. The center of this bowed section can be supported by a brace connected to the supporting structure, although this has been found to be unnecessary. Also more than 1 take-up loop can be used if needed.

With a substantially continuous guide loop adjusted to the length of the handrail so that static tension is not required to maintain the handrail in the guide loop, the handrail can be pushed as well as pulled around the closed loop through the utilization of much lower forces at any particular point on the handrail than was required in the prior art systems. The coefficient of friction of the nylon strips ranges from 0.18 to 0.50 depending upon the load. It has been found that when the handrail can be both pushed and pulled, so that the loading at any particular point in a handrail is low, the system will operate in the 0.18range. However, when the handrail is under static tension so that it can only be pulled around the guide loop the loading on the handrail is much higher and the system operates in the 0.50 range. It can be seen therefore that thetotal force required to move the handrail under this system is only one-third of that required to move the handrail in the prior art system. It can be appreciated that a reduction in the loading on the handrail will increase its life. Since the force applied to the handrail is divided between a pushing and a pulling force the loading at any particular point of the handrail is therefore even less than onethird that applied by the prior arts systems.

According to this invention, the handrail may be driven by any suitable driving means which can apply both a pushing and pulling force and which does not require that the entire handrail be under tension. The type of drive disclosed in the application of Myron A. Clark, Ser. No. 511,165, filed Dec. 2, 1965 and assigned to the same assignee, now US. Pat. No. 3,414,109 is suitable for this purpose. According to that system the driving force is applied to the handrail by a series of drive wheels 53. As can be seen from the sectional view of 7 FIG. 5 each drive wheel 53 is mounted on a shaft 63 which is journaled in a bearing 65. A sprocketwheel 55 connected to the other end of the shaft 63 imparts a rotating motion to the wheel 53 in response to movement of a chain 59. The chain 59 passes over the sprocket wheel'of each of the drive assemblies. The chain 59 also passes over a sprocket wheel 71 which is connected to the sprocket wheel 4 on the conveyor so that the drive assemblies are rotated by the motor 6 The gearing is such that the handrail is driven in synchronism with the conveyor. ldler sprockets 61 serveas guides for the chain 59. A pressure roller 57 rotatably mounted on a shaft 67 below each drive wheel serves to hold the inside of the base portion of the handrail in tractional engagement with the drive wheels 53. Preferably the rim of the guide wheel 53A is constructed of an elastomer for better frictional engagement with the handrail. The driving mechanism as well as the flexible portion of the guide means are located below the balustrade and are hidden from view in normal use by the skirt 39.

Although the flexible portion of the guide means is shown visibly fastened at one end and adjustable at the other it is to be understood that this portion of the guide means could be adjustably fastened at both ends. It should also be understood that an expandable connection could be provided to fill the gap 11h, however, it has been found not to be necessary if the gap is kept within reasonable limits.

FIG. 6 illustrates a modification of the handrail guide for use with a transparent balustrade. The solid extrusion 41 having a base 41a and two vertical projections 41b supporting horizontal flanges 41c serves as a guide for the handrail and as the upper portion of the balustrade. A notch 41d in the lower portion of the base 41a, receives the top edge of the transparent vertical portion of the balustrade 43. In this configuration the guide 41 would be supported at various points along its length by vertical posts as shown in US. Pat. No. 3,283,878. This extruded guide member can also be bent to form the curved end portions. I

What we claim is:

1. A passenger conveyor system comprising a supporting structure, a continuous load bearing conveyor mounted on the supporting structure, a balustrade vertically mounted on the supporting structure adjacent the conveyor and extending a substantial length along the conveyor, substantially continuous guide means extending along the upper surface of the balustrade, vertically downward near the ends of the balustrade and thence along the supporting structure under the balustrade to form a substantially closed guide loop, said guide means being substantially stationary and nonrotating with respect to the supporting structure, a continuous flexible belt supported by the guide means, said guide means being continuous to the extent that any gaps therein are bridged by said flexible belt such that the natural stiffness of said flexible belt maintains the guide direction of said guide means across the gap without lateral movement of the belt even when pushed across the gap, and drive means coupled to a portion of said continuous flexible belt for applying both a pushing and pulling force to said belt, said substantially continuous guide means terminating in close proximity to either side of said drive means to provide in combination with the drive means restraint against movement transverse to the directionof travel of the belt under the pushing force applied by said drive means whereby the continuous belt is pushed as well as pulled around the guide loop.

2. The passenger conveyor of claim 1 wherein said continuous belt has a generally C-shaped cross-section with the opening of the C oriented toward the center of the loop and wherein said guide means comprises substantially stationary continuous flanges oppositely disposed transverse to the direction of movement of the continuous belt for engaging said C-shaped belt and preventing it from being raised or transversely disengaged from the guide means.

3. The passenger conveyor of claim 2 wherein the length of the guide loop formed by the continuous flanges is such that the C-shaped belt fits loosely over the flanges and wherein the drive means includes means for applying a driving force to the belt in the absence of static tension on the belt.

4. The passenger conveyor of claim 2 wherein said drive means comprises a driving sheave rotatably mounted for engagement on one surface of the continuous belt, a pressure roller rotatably mounted for engagement of the other surface of the continuous belt adjacent the driving sheave for forcing said belt into tractional engagement therewith and motive means for rotating said driving sheave.

5. The passenger conveyor of claim 2 including adjusting means for adjusting the length of the guide loop formed by the stationary guide means to compensate for variations in the length of the continuous belts utilized whereby the substantially continuous guide means can be adjusted to the exact length of the particular belt used.

6. A passenger conveyor system comprising a supporting structure, a continuous load bearing conveyor mounted on the supporting structure, a balustrade vertically mounted on the supporting structure adjacent the conveyor, substantially continuous guide means extending along the upper surface of the balustrade, vertically downward near the ends of the balustrade and thence along the supporting structure under the balustrade to form a substantially closed guide loop, said guide means being substantially stationary and nonrotating with respect to the supporting structure, a continuous flexible belt supported by the guide means, said continuous belt having a generally C-shaped cross-section with the opening of the C oriented toward the center of the loop and wherein said guide means cornprises substantially stationary continuous flanges oppositely disposed transverse to the direction of movement of the continuous belt for engaging said C-shaped belt and preventing it from being raised or transversely disengaged from the guide means, adjusting means for adjusting the length of the guide loop formed by the stationary guide means to compensate for variations in the length of the continuous belt utilized whereby the substantially continuous guide means can be adjusted to the exact length of the particular belt used, said ad- 'justing means comprising a flexible portion of said guide means with sufficient stiffness that it will retain its shape when bowed, mounting means for fastening the ends of said flexible portion to the supporting structure, said mounting means including adjustable mounting means for, fastening one end of said flexible portion of the guide means to the supporting structure with a variable amount of longitudinal displacement between said flexible portion and the adjacent portion of said guide means, and drive means coupled to a portion of said continuous flexible belt for applying both a pushing and pulling force to said belt, said substantially continuous guide means terminating in close proximity to either side of said drive means to provide in combination with the drive means restraint against movement transverse to the direction of travel of the belt under the pushing force applied by said drive means whereby the continuous belt is pushed as well as pulled around the guide loop.

7. The passenger conveyor of claim 6 wherein the adjustable mounting means includes a plate having a slot oriented parallel to the longitudinal axis of the guide means fastened to said supporting structure and fastening means connected to the flexible portion of the guide means and passin through said slot for clamping said flexible portion 0 the guide means to said p ate said fastening means being slidable in said slot to adjust the position of said flexible portion of the guide means with respect to the plate.

8. The passenger conveyor of claim 2 including U- shaped strips of low friction material clamped over the flanges of the continuous guide member.

9. The passenger conveyor of claim 8 wherein the oppositely disposed flanges are independently supportedby legs radiating from the balustrade and the supporting structure transverse to the direction of movement of the continuous belt and wherein one arm of each U-shaped strip is elongated and curved inward at the free end to form a lip, said elongated arm being equal in length to the width of the flange whereby the lip of the U-shaped strip can be snapped over the inner edge of said flange to firmly hold the U-shaped strip in place. 

1. A passenger conveyor system comprising a supporting structure, a continuous load bearing conveyor mounted on the supporting structure, a balustrade vertically mounted on the supporting structure adjacent the conveyor and extending a substantial length along the conveyor, substantially continuous guide means extending along the upper surface of the balustrade, vertically downward near the ends of the balustrade and thence along the supporting structure under the balustrade to form a substantially closed guide loop, said guide means being substantially stationary and non-rotating with respect to the supporting structure, a continuous flexible belt supported by the guide means, said guide means being continuous to the extent that any gaps therein are bridged by said flexible belt such that the natural stiffness of said flexible belt maintains the guide direction of said guide means across the gap without lateral movement of the belt even When pushed across the gap, and drive means coupled to a portion of said continuous flexible belt for applying both a pushing and pulling force to said belt, said substantially continuous guide means terminating in close proximity to either side of said drive means to provide in combination with the drive means restraint against movement transverse to the direction of travel of the belt under the pushing force applied by said drive means whereby the continuous belt is pushed as well as pulled around the guide loop.
 2. The passenger conveyor of claim 1 wherein said continuous belt has a generally C-shaped cross-section with the opening of the C oriented toward the center of the loop and wherein said guide means comprises substantially stationary continuous flanges oppositely disposed transverse to the direction of movement of the continuous belt for engaging said C-shaped belt and preventing it from being raised or transversely disengaged from the guide means.
 3. The passenger conveyor of claim 2 wherein the length of the guide loop formed by the continuous flanges is such that the C-shaped belt fits loosely over the flanges and wherein the drive means includes means for applying a driving force to the belt in the absence of static tension on the belt.
 4. The passenger conveyor of claim 2 wherein said drive means comprises a driving sheave rotatably mounted for engagement on one surface of the continuous belt, a pressure roller rotatably mounted for engagement of the other surface of the continuous belt adjacent the driving sheave for forcing said belt into tractional engagement therewith and motive means for rotating said driving sheave.
 5. The passenger conveyor of claim 2 including adjusting means for adjusting the length of the guide loop formed by the stationary guide means to compensate for variations in the length of the continuous belts utilized whereby the substantially continuous guide means can be adjusted to the exact length of the particular belt used.
 6. A passenger conveyor system comprising a supporting structure, a continuous load bearing conveyor mounted on the supporting structure, a balustrade vertically mounted on the supporting structure adjacent the conveyor, substantially continuous guide means extending along the upper surface of the balustrade, vertically downward near the ends of the balustrade and thence along the supporting structure under the balustrade to form a substantially closed guide loop, said guide means being substantially stationary and non-rotating with respect to the supporting structure, a continuous flexible belt supported by the guide means, said continuous belt having a generally C-shaped cross-section with the opening of the C oriented toward the center of the loop and wherein said guide means comprises substantially stationary continuous flanges oppositely disposed transverse to the direction of movement of the continuous belt for engaging said C-shaped belt and preventing it from being raised or transversely disengaged from the guide means, adjusting means for adjusting the length of the guide loop formed by the stationary guide means to compensate for variations in the length of the continuous belt utilized whereby the substantially continuous guide means can be adjusted to the exact length of the particular belt used, said adjusting means comprising a flexible portion of said guide means with sufficient stiffness that it will retain its shape when bowed, mounting means for fastening the ends of said flexible portion to the supporting structure, said mounting means including adjustable mounting means for fastening one end of said flexible portion of the guide means to the supporting structure with a variable amount of longitudinal displacement between said flexible portion and the adjacent portion of said guide means, and drive means coupled to a portion of said continuous flexible belt for applying both a pushing and pulling force to said belt, said substantially continuous guide means terminating in close proxImity to either side of said drive means to provide in combination with the drive means restraint against movement transverse to the direction of travel of the belt under the pushing force applied by said drive means whereby the continuous belt is pushed as well as pulled around the guide loop.
 7. The passenger conveyor of claim 6 wherein the adjustable mounting means includes a plate having a slot oriented parallel to the longitudinal axis of the guide means fastened to said supporting structure and fastening means connected to the flexible portion of the guide means and passing through said slot for clamping said flexible portion of the guide means to said plate, said fastening means being slidable in said slot to adjust the position of said flexible portion of the guide means with respect to the plate.
 8. The passenger conveyor of claim 2 including U-shaped strips of low friction material clamped over the flanges of the continuous guide member.
 9. The passenger conveyor of claim 8 wherein the oppositely disposed flanges are independently supported by legs radiating from the balustrade and the supporting structure transverse to the direction of movement of the continuous belt and wherein one arm of each U-shaped strip is elongated and curved inward at the free end to form a lip, said elongated arm being equal in length to the width of the flange whereby the lip of the U-shaped strip can be snapped over the inner edge of said flange to firmly hold the U-shaped strip in place. 